This invention relates to electric busway assemblies and in particular to joint assemblies for facilitating the connection of a bus duct having one or more runs to a bus duct having a different number of runs.
Electrical busway systems are used for distribution of electrical power, especially for power systems having high current ratings. These systems normally employ elongated duct-type housings which enclose a plurality of parallel bus bars, the assemblies being termed bus ducts. The ducts are manufactured in sections of predetermined length for convenience of transportation, handling and installation. Generally these sections are mounted end to end with the bus bars of connecting sections in electrically conductive contact with each other via a joint assembly. An exemplary general arrangement for such a joint assembly is shown in U.S. Pat. No. 3,786,394, now assigned to the assignee of the present invention.
Systems to be applied in particularly high current applications often employ multiple parallel bus duct runs. This is generally done when the current carrying capabilities of individual bus bars would be exceeded by the expected or rated current load. An assembly for connecting the bus bars in the same phase of the various runs of a multiple run bus duct so as to prevent localized overcurrent conditions, referred to hereinafter as a "phase collector", is disclosed in U.S. Pat. No. 3,818,417, now assigned to the assignee of the present invention. Thus, in an application where the total expected or rated current in each individual phase is greater than a single bus bar is capable of carrying, more than one bus bar is supplied per phase, and phase collectors are provided to balance the phase among the bus bars carrying each individual phase.
Frequently the need arises to connect a bus duct having a certain number of runs to a bus duct having a different number of runs. This need arises most commonly in an application where it is desired to reduce the bus duct current rating, such as for short distance power tap-offs. For example a triple run duct may be connected to a double run duct, or a double run duct to a single run duct, or a triple run duct to a single run duct, or any other such arrangement. In the past, this connection was accomplished by use of an unfused reducing section, the length of which was simply that of one of the shorter regular sections. The reducing section was assembled with sufficient runs to match the duct having the larger number of runs, and connected to the load end of the section with the larger number of runs by the same means used to connect identical sections. One or more of the runs of the unfused reducing section was simply terminated, with phase collectors connecting the bus bars within each phase as referred to above. The end of the reducing section connected to the source end of the duct having the lower number of runs was then also connected by the usual means, being configured to match that duct. Such an unfused reducing section has certain disadvantages, however, relating particularly to all the extra parts required, including but not limited to extra plug-in joints, extra phase collectors and insulators, and the extra sheet metal and labor required.
This invention relates to improvements to the apparatus described above and to solutions to the problems raised thereby.